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Paper: Low-Frequency Solar p Modes as Seen by the GOLF and GONG Instruments
Volume: 416, Solar-Stellar Dynamos as Revealed by Helio- and Asteroseismology: GONG 2008/SOHO 21
Page: 329
Authors: Salabert, D.; García, R. A.
Abstract: In the case of spatially-revolved helioseismic data (such as Michelson Doppler Imager (MDI), Global Oscillation Network Group (GONG), Helio- seismic and Magnetic Imager (HMI)), the usual mode-fitting analysis consists of fitting the 2l+1 individual m-spectra of a given multiplet (n,l) either individually or simultaneously. Such fitting methods fail to obtain reliable estimates of the mode parameters (frequency, splitting, ...) when the signal-to-noise ratio (SNR) is low, which makes those methods not suitable when one wants to look at the low-amplitude, long-lived solar p modes in the low-frequency range. Instead, Salabert et al. (2007) developed a new method to extract the mode parameters by adjusting the rotation- and structure-induced frequency shift for each m-spectrum to minimize the mode width in the m-averaged spectrum (a "collapsogram"). The m-averaged spectrum technique, applied to the spatially-resolved GONG and MDI data, appeared to be a powerful tool for low Signal to Noise Ratio (SNR) modes in the low-frequency range. Another possibility to increase the SNR is to combine data from different instruments (García et al. 2004a). We present here an adaptation of both techniques: the "collapsograms" applied to a combination of observations from a Sun-as-a-star instrument, Global Oscillations at Low Frequencies (GOLF), and a disk-imaged one, GONG.
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